Various communication standards, such as digital subscriber line (xDSL), very-high-bit-rate digital subscriber line 2 (VDSL2), G.hn, and G.fast, have been proposed or developed to provide high-speed data transmission from the service provider (e.g., a central office) to a customer premise over the existing twisted-pair copper wiring conventionally used for telephone service. Such technologies leverage modem technology to increase the data transfer bandwidth of the twisted-pair copper wiring. Typically, modems are provided on the ends of the subscriber line copper wiring to communicate between the central office and the customer premise. The manner in which the two modems communicate is established by the particular standard governing the communication. Because the existing telephone wire is used, the data signals are typically transferred out-of band with the voice band signals. Because different frequencies are used for the voice band and the data band, voice and data information can be concurrently transferred over the twisted-pair copper line.
Service providers have increased data bandwidth by installing fiber optic cabling between the central office (CO) and a distribution point unit (DPU) closer to the customers. A particular DPU may interface with a bundle of twisted pairs to service a relatively small number of customer premise connections. This approach shortens the length of the copper pair between the CO interface at the DPU and the customer, thereby allowing increased data rates. Thus the DPU will provided telephony and/or data to one or more customer premises equipment (CPE)
One difficulty arising from an optical connection between the central office and the DPU lies in the inability to provide a source of power for the DPU. Due to the remoteness of the DPU with respect to the central office, a local power supply is often unavailable or expensive to install.
Power for a DPU may be provided by reverse power feeding, wherein power is supplied to the DPU from the various CPEs for which telephony and/or data services are provided from the DPU. A standard for reverse power feeding is being standardized by ETSI and the Broadband World Forum. In such an embodiment, a power supply in the DPU may combine power contributions from multiple CPEs to power a main distribution unit (MDU) that handles the voice and data communication. This arrangement is referred to as a reverse power system, since the CPEs are the PSE and the DPU, particularly the MDU, is the powered device (PD).
The CPE PSE thus injects power across the copper pair. In order to use a plain old telephony service (POTS) type analog telephone, a POTS adapter is to be installed between the copper pair and the POTS telephone. FIG. 1 illustrates a high level block diagram of such a reverse power feeding arrangement 10, reverse power feeding arrangement 10 comprising a DPU 20 and a CPE 30 connected by a copper pair 40, with certain standard ETSI symbols shown. DPU 20 comprises: a data provision module 50, typically in optical communication with a CO; a power extraction circuitry 60; a signature resistor 70; an electronically controlled switch 80; a voltage detection circuitry 90; a classification current circuitry 100; an under voltage lock-out (UVLO) circuitry 110; an electronically controlled current path 120; a capacitor 130; and a DC/DC converter 140. In one non-limiting embodiment, electronically controlled current path 120 is implemented as an n-channel metal-oxide-semiconductor field-effect-transistor (NFET), and will be described herein as such.
Data provision module 50 and a first terminal of power extraction circuitry 60 are each connected to copper pair 40 past the U-O reference point. The U-O reference point is defined as the reference point at the DPU containing both DC power and service data. A second terminal of power extraction circuitry 60 is coupled to a first end of signature resistor 70, a first terminal of voltage detection circuitry 90, a first terminal of classification current circuitry 100, a first terminal of UVLO circuitry 110, a first end of capacitor 130 and a first terminal of DC/DC converter 140, the line denoted OUT. A third terminal of power extraction circuitry 60 is coupled to a first end of electronically controlled switch 80, a second terminal of voltage detection circuitry 90, a second terminal of classification current circuitry 100, a second terminal of UVLO circuitry 110 and the source of NFET 120, the line denoted RET. The gate of NFET 120 is coupled to an output of UVLO circuitry 110. The drain of NFET 120 is coupled to a second end of capacitor 130 and a second terminal of DC/DC converter 140. Electronically controlled current path 120 is illustrated and described herein as being coupled within return line RET, however this is not meant to be limiting in any way. In another embodiment, electronically controlled current path 120 is coupled within output line OUT, without exceeding the scope. A third terminal of DC/DC converter 140, denoted DC, is coupled to data provision module 50.
CPE 30 comprises: a PSE 150; a power splitter 160; a service splitter 170; a POTSA-D adaptor 180; and a POTS telephone 190. PSE 150 is connected to power splitter 160 across the U-R2P reference point, defined as the reference point at CPE 30 containing the injected DC power. Power splitter 160 is connected to service splitter 170, which provides service and optionally analog phone service for CPE 30. Power splitter 160 is additionally connected to copper pair 40 across the U-R reference point, defined as the reference point at CPE 30 containing both DC power and service data. POTSA-D 180 is connected to copper pair 40 between power splitter 160 and the U-R reference point across the U-R2S reference point, defined as the CPE reference point containing the baseband POTS and the converted POTS signaling. POTSA-D 180 is an adapter that can be attached to one or more POTS telephones 190 in CPE 30. POTSA-D 180 is arranged to perform the following functions: translate the signals from the upstream DC and low frequency POTS signaling from the POTS telephone 190 into an in-band or out-of-band signaling system; translate the signals from the downstream in-band or out-of-band signaling system into POTS signaling towards the POTS telephone 190; and provide sufficient current, with a current limit, and DC voltage to supply POTS telephone 190.
In operation, in a detection stage, PSE 150 outputs a plurality of different detection voltages in order to determine whether a valid signature resistance is presented by DPU 20. The detection voltages are in one embodiment greater than 10 Volts. The voltages are extracted from copper pair 40 by power extraction circuitry 60. The resistance of signature resistor 70 is determined responsive to the output voltage values, as known to those skilled in the art at the time of the invention. As illustrated, electronically controlled switch 80 is coupled in series with signature resistor 70 and is initially set to be open. Responsive to detection by voltage detection circuitry 90 that a detection voltage has been presented thereacross, voltage detection circuitry 90 closes electronically controlled switch 80, thereby presenting the detection voltages across signature resistor 70. PSE 150 then detects whether signature resistor 70 exhibits a valid signature resistance. In the event that a valid signature resistance is not detected, no power is provided by PSE 150, as known to those skilled in the art at the time of the invention. Voltage detection circuitry 90 detects that a detection voltage is no longer applied to DPU 20 and responsive thereto opens electronically controlled switch 80. This removes the resistance of signature resistor 70 from the circuit to avoid unnecessary waste of power and to avoid affecting any classification current (described below).
In order to provide more efficient reverse power feeding, it is advantageous for PSE 150 to determine the class of DPU 20. Particularly, in a classification stage, PSE 150 is arranged to generate a classification voltage, which is presented to DPU 20, and classification current circuitry 100 is arranged to generate a classification current whose magnitude is indicative of the class of DPU 20. PSE 150 is then arranged, responsive to the magnitude of the received classification current, to determine the class of DPU 20 and adjust the current limit accordingly.
In the event that POTS telephone 190 is mistakenly connected to the reverse power feeding network without POTSA-D 180, i.e. POTS telephone 190 is mistakenly connected directly to the in-premises wiring at the potential of reference point U-R, when POTS telephone 190 is off-hook it draws a large current from PSE 150. It is therefore important that PSE 150 be able to detect an off-hook condition of POTS telephone 190, as described in U.S. Pat. No. 9,374,452, issued Jun. 21, 2016 to Peker et al., the entire contents of which are incorporated herein by reference. It is particularly important to detect an off-hook condition POTS telephone 190 during start-up so excess current won't be supplied by PSE 150. However, during start-up a large inrush current is drawn by capacitor 130, which can mask an off-hook condition of POTS telephone 190. As a result, the PSE won't detect the off-hook condition and after the inrush current stabilizes a large current will still be drawn from PSE 150 by the off-hook POTS telephone 190.